Apple today announced that the next version of its Mac OS will be available to download on its Mac App Store from tomorrow.
The latest update pushes integration with Twitter, Facebook and a range of other services to a new level with one click updates to these services. Along with further integration with iOS including reminders, notes, iMessage and much more... in fact 200 more.

It'll be available for just $19.99 in the US and £13.99 in the UK. We'll have to wait until the evening in the UK though as these updates usually become live around midday US time.